| Transparent conducting oxides (TCOs) films are widely used in many photoelectric d eVices, such as solar cells, heat mirrors, surface acoustic wave d eVices and liquid-crystal as transparency electrodes, which is due to their wide band gaps, high conductivity and high transmittance in the visible region and high reflectivity in infrared region. Most of the unintentional doped TCOs films are n-type semiconductors due to the intrinsic defects, such as interstitial atoms, oxygen vacancies and anti-position atoms, which restrains their application badly. If p-type TCOs can be fabricated, there will be a breakthrough in the small-scale high performance components, such as white LED, ultraviolent LED and circuits with low power, and in the large-scale components, such as large-scale LED, transparent solar cells and reflective infrared glasses and so on.SnO2 is a wide direct band gap semiconductor material and compared with other materials, it has many advantages such as a wider band gap of 3.6-4.0 eV, higher exciton binding energy of 130 m eV (-3.3 eV and 60m eV for ZnO, respectively), lower growth temperature and higher chemical stability. As an important part of the research of transparent conducting and sensor materials, the fabrication and properties investigation of SnO2 and doped SnO2 films have made a rapid progress in recent years. In theory, the conduction type can be changed by IIIA element doping. Until now, few reports have been published on the properties of gallium doped films and gallium and nitrogen co-doped SnO2 films prepared by MOCVD. In this paper, SnO2:Ga and SnO2:Ga-N films were fabricated by MOCVD, and the effect of doping on the structural and opto-electrical properties of the films are being investigated in detail.The major work and results are as follows:1. SnO2:Ga films with various concentration of gallium were fabricated on sapphire (0001) using a MOCVD system. High purity tetraethyl tin (C2H5)4Sn was employed as Sn organometallic (OM) source, trimethyl gallium (CH3)3Ga as Ga OM source, O2 as oxidant and N2 as carrier gas. The structural, optical and electrical properties of samples were investigated in detail. The XRD spectra show that all films have the rutile structures of SnO2 and have a high degree preferred orientation along a-axis. Measurement of transmittances has been taken in the wavelength range of 200-900 nm. The optical band gaps of films can be obtained according to the (ahv)2～hv plots, and they varied with the content of dopant. The PL spectra of 3% and 15% doped SnO2:Ga films were discussed in detail. The energy 1 eVel of interstitial Ga acting as donor is 0.12 eV below the bottom of conduction band, and 0.25 eV above the valence band maximum for the substitutional Ga for Sn serving as acceptor. The electrical properties of the samples varied with the doping. Also, the effects of annealing on the properties of films were investigated in the paper.2. Ga and N co-doped SnO2 films were deposited onα-Al2O3 by MOCVD. Sn and Ga OM sources were the same as above. NH3 was used as N resource. The as-deposited films were annealed for 2 h in nitrogen at different temperatures. XRD, SEM and transmittance were performed, and structural and optical properties were discussed. In addition, by comparing the properties of Ga and N co-doped films with Ga doped films, the effect of N on the properties of the films were investigated.
|
PDF Full Text Request